Transducer assembly for reverberative delay lines



p 1966 J. B. BROMBAUGH ETAL 3,24,2G

TRANSDUCER ASSEMBLY FOR REVERBERATIVE DELAY LINES Filed Aug. 18, 1961 INVENTORS JoHM B.%E.MBAU6-H C?" EDWARD M. JoMEs ATTORNEYS United States Patent 3,246 264 TRANSDUCER ASSEMBLI FUR REVERBERATIVE DELAY LINES John B. Bromhaugh and Edward M. Jones, Cincinnati,

Ohio, assignors to D. H. Baldwin Company, a corporation of Ohio Fires Aug. 18, 1961, Ser. No. 132,418 Claims. (Cl. 333-) The present invention relates generally to electromechanical and to mechanico-electrical transduction in delay lines and reverberators, and more particularly to devices and methods for coupling transducers to long wire mechanical delay lines, for mechanically mounting the delay lines, for effective generation of transverse mechanical waves on the delay lines and for effective translation of mechanical waves into electrical signals.

Long wires, preferably in the form of helical springs, are useful for generating reverberation effects, in music, approximating acoustic reverberations produced by the acoustic properties of large reverberant spaces. Such reverberation generators may be operative at sonic frequencies or at ultrasonic frequencies. In the former case the output of an electrical musical instrument, such as an electronic organ, or of a phonograph, tape, recorder, or other source of electrical signals representative of music, is directly coupled to a driver electro-mechanical transducer which provides mechanical vibrations in the wire. A mechanico-electrical transducer is coupled to the Wire at a point remote from the driver for translating the vibrations into electrical signals suitable for subsequent electro-acoustic transduction. The structural arrangement of the system is such that multiple reflections occur at the transducers or at other selected points along the wire.

In the alternative, electrical signals representative of music are modulated on an ultrasonic carrier, or are heterodyned to fall in the ultrasonic range, and the converted signals are employed to generate reverberative mechanical vibrations on a wire at one point of the wire. The vibrations are transduced to electrical signals at a remote point along the wire and the electrical signals, with reverberative effects now added, are derived from the carrier by frequency conversion.

The present invention concerns itself primarily with ultrasonic reverberation systems, in terms of a preferred application. The invention, however, finds further application to sonic reverberators, to mechanical filters, to mechanical delay lines, and the like.

Briefly describing a preferred embodiment of the invention, an elongated piezo-electric transducer is end mounted in a rigid support, and the end of a wire delay line which is to be driven by the transducer is end mounted in the same rigid support. A linkage or coupling element is provided between a point of the delay line separated by approximately wave length from the support, and a suitable point of the transducer. The coupling element may be formed of resilient material, may be much thinner in diameter than the wire, and may have a slight bend therein. The stifiness of the coupling wire is sufficient for transfer of vibrations from the transducer to or from the wire, but the existence of a bend in the wire, the small diameter of the wire, and its general stiffness are such that the coupling element gives by bending in response to a strong shock or impact, and does not transfer a shock or impact to the transducer. Thereby effective vibrational coupling occurs between the wire and the transducer without the danger of destroying the transducer through shock or impact applied to the wire.

In a modification of the just described invention, the wire is mounted or secured to the rigid element by means of a clamp secured to the wire approximately wavelength from the end thereof, instead of at the end, and

Patented Apr. 12, 1966 the coupling element drives the wire at or adjacent to its end, instead of A wavelength from the end.

In the two above briefly described modifications of our invention, accordingly, the crystal drives the wire or is driven by the wire through a coupling element or linkage which is incapable of transmitting shocks but is capable of transmitting vibrations. Where the wire is mounted remotely from its end the wire may be connected to the linkage at its end, while if the wire is end mounted the linkage may be connected to the wire remotely from the end, but in each case the distance between the mounting and the linkage point is preferably approximately wavelength long, which provides a low impedance driving point at the wire.

In accordance with further modifications of the invention the wire is secured to a relatively massive semi-rigid vibratory member, to which the transducer may be either directly cemented, or coupled by means of a linkage, but in any event the transducer is isolated from the wire in respect to shock and impact because of its association with the massive semi-rigid element. The massive seml rigid element may be the sole protective feature or it may supplement the protection afforded by a suitable linkage.

It is, accordingly, a primary object of the present invention to provide a novel reverberator.

It is another object of the present invention to provide a novel electro-mechanical transducer system and a novel mechanico-electrical transducer system.

A further object of the invention resides in the provision of a transducer capable of transducing mechanical waves to and from an elongated wire delay line, wherein the transducer is isolated or decoupled from the delay line in respect to impact and shock, but is capable of imparting ultrasonic vibrations to the delay line or of transferring the ultrasonic vibrations from the wire to the delay line.

A further object of the invention resides in a provision for associating a transducer and a long wire delay line, wherein the wire and the delay line are individually mounted in a rigid element, and are coupled by means of a flexible linkage capable of protecting the transducer from impact and shock imparted to the wire, and also capable of effecting desired impedance transformations between the wire and the transducer.

Still another object of the invention resides in the provision of a mounting for a transducer and an elongated wire delay line, wherein a massive semi-rigid element is interposed between the transducer and the wire, the transducer being either mounted on the semi-rigid element or coupled thereto by means of a linkage, so that the transducer is mechanically isolated in respect to impact and shock originating in the Wire by the semi-rigid member.

The above and still further features, objects and advantages of the present invention will become apparent upon consideration of the following detailed description of several preferred embodiments thereof, especially when taken in conjunction with the accompanying drawing wherein:

FIGURE 1 is a view in perspective of a first embodiment of the invention.

FIGURE 2 is a view in plan of the structure of FIG- URE 1.

FIGURE 3 is a view in plan of a modification of the structure of FIGURE 1, and

FIGURES 4, 5 and 6 are views in plan of structures for mounting transducers and wire delay lines by means of an interposed semi-rigid element capable of protecting the transducers from shock and impact imparted to the wires.

Referring now more particularly to accompanying drawings, the reference numeral 1 denotes a rigid mounting block through which extend a pair of cylindrical openings 1a and 1b, preferably extending parallel to one another. Extending through one of the openings, 10, is the end of a wire Zcoiled in the form of a helical spring, and functioning as a delay line, as in a reverberation generator for music. The line consists essentially of a wire coiled into the form of a helical spring, but the mode of propagation of the vibratory wave is transverse' in the wire itself, so that the spring vibrates as a long wire, rather than as a spring. The helical form of the spring is thus not important except as a device for conserving space. The end of the wire 3 which extends into the opening 1a is cemented'or soldered internally of the opening. Preferably the cement extend-s throughout the opening, so that acoustically the Wire sees the mounting block 1 as if the wire were terminated at the mounting block, and accordingly the wire appears to be terminated in infinite impedance. The element 4, which extends through the opening 1b, constitutes a piezo-electric transducer, preferably of the ceramictype. That part of the piezo-electric transducer 4 which extends within the opening 1b may be electrically insulated-from the material of the mounting block 1 if, the latter is metallic. The length of the transducer 4-, taken perpendicularly of the mounting block, i.e. the free length of the transducer, is selected to provide the greatestoutput consistent with a flatfrequency response in the region of the operating frequency. In the case of a supersonic. delay line the driving signal may constitute a relatively wide bend of frequencies centered aroundZO kc, and the transducer 4' must be capable of responding over the entire band with approximately equal response to all the frequencies of theband. Further, it must be resonant over the band in order 'to obtain maximum amplitude of response.

A mechanical link 5 joins the point of the transducer to a point ofv the Wire. This link may be slightly bent, so that it does not provide a rigid link in response to shock, but is readily capable of giving or further bending in response to shock. Yet its stiffness must be sufficient to enable it to trans-fer supersonic vibrations from the transducer to the wire. The shape and position of the link is very importantin determining itseffect on the reverberation line. If the link is relatively small, say .010 diameter phosphor bronze, it transmits very little shock to the driver from the spring, the latter being preferably .040 diameter BeCu wire. By moving the connection of the link along the spring from the mounting block to a length away from the block equal to wavelength of the soundwave in the wire, it is possible to couple into mechanicalimpedance from nearly infinity to a value near the characteristic impedance, in accordance with transmission line theory. Changing the length and diameter of the link also effects its empedance transformation properties in accordance with transmission line theory. By adjusting the three parameters it is possible to select a coupling between the spring and the driver which will give high output and a reflection factor conducive to a desirable reverberation time.

A preferred'point of connection of the link to the wire is at a point A wavelength from the mounting block 1. The point of connection to the transducer may be inwardly of the end of the transducer, but the point of connection to the transducer need not be either wavelength. or /2 wavelength or any specific number of Wavelengths from the mounting block, since the transducer vibrates not as a transmission line but as a lumped circuit, when treating the mechanical phenomena by analogy to transmission line theory. The problem is therefore one of driving the wire, which constitutes a transmission line, by means of a lumped circuit, representing the transducer, through a coupling link representingthe link 5. The latter provides impedance matching in terms of its location on the transducer and in terms of its diameter relative to the diameter of the spring itself.

One of the primary advantages of the construction illustrated in FIGURES 1 and 2 of the accompanying drawings is the rugged construction of the system, and its freedom from shock transmission to the piezoelectric transducer, and in addition its versatility in coupling between the transducer and the delay line. Ceramic transducers are very fragile elements and in the present case are very small, since the system may be designed to operate in the 20 kc. region. Accordingly, any construction which can transmit shocks to the crystal or which can impart large bending moments to the crystal, is likely in the course-of commercial utilization of the invention to fracture the crystal. It is of primary importance that this possibility be avoided.

Referring now more particularly to FIGURE 3 of the accompanying drawings, the reference numeral 10 denotes a'rigidsolid mounting block having an opening 11 with-in which is cemented the end of a piezoelectric transducer 12, preferably ceramic. A clamp 13 is likewise secured to the mounting block 10, preferably by inserting the end of the clamp into an opening in the mounting block 10. The clamp 13 may consist of a small plate extending at right angles to the crystal 12, for convenience of construction. The clamp 13 includes anopening 14, through which extends the end of a wire delay line 15', which is to be vibrated in transverse mode by setting up vibrational Waves along the length of the wire 15. For convenience, the wire 15 may be coiled into the form of a helical spring. The clamp 13 is arranged to have at least ldegnee of freedom, i.e. the clamp 13 must be free to vibrate in a plane transversely of its length in order to permit transverse vibrations to pass from one side to the other of the clamp 13. The end of the wire 15 extends beyond theclamp 13 for a distance of A wavelength at the operating frequency of the system, i.e. at'the wavelength of the transverse vibrations of the wire 15. A linkage 17 is provided,

which extends between a point-18- on the transducer and a point 19 at or adjacent the wire end, the point of attachment to the wire end being at A wavelength from the clamp 13, but the point of connection to the transducerbeing essentially unrelated to the Wavelength involved since the transducer vibrates as a lumped circuit while the transverse Waves passing along the wire operate as if the wire were a transmission line. The linkage 17 is slightly bent to prevent transmission of shock waves from the Wire to the transducer and the point of transmission of connection of the linkage 17 to the transducer 12, i.e. the location of the point 18, is selected in accordance with the same criteria as obtained in the case of the embodiment of our invention illustrated in FIGURES 1 and 2 of the accompanying drawing, and which have been herein above described.

The clamp 13 can locate the spring quite rigidly with respect to the mounting block 10, but it must permit the passage of high frequency transverse vibrations. For'this purpose the clamp 13 must be free to pivot as on a fulcrum, transmitting changes of angle of the wire by lever action.

The distinction between the embodiments of our invention illustrated in FIGURES l and 2, and that illustrated in FIG. 3, res-ides primarily in the fact that in FIGURES l and 2. the wire is clamped at its end and driven at a point Wavelength from its end, while in the case of FIGURE 3 the wire is driven at its end and is clamped wavelength away from the driving point.

While the description of operation of the present system has proceeded on the basis that the wire is driven wavelength away from its mounting point, Whether that point he the end of the wire or a point displaced from the end of the Wire, this A wave relationship is not critical, but is merely a preferred and most efiicient driving point. As is true, when one is driving an electrical transmission line, as also in the acoustical. case the separation between the driving point and the clamping point, may be slightly less or more than wavelength.

While piezo-electric transducers may be cemented directly to the long wire delay line, or may be coupled to such a delay line through a simple linkage as in embodiments of our inventions illustrated in FIGURES l to 3, inclusive, considerable advantage is derivable if the transducer is divorced from direct association with the delay line, and instead is coupled to a relatively massive semi-rigid structure capable of transferring vibrations, the latter being secured at one end to a rigid structure and at its other end to an end of a wire delay line. The major advantage of this construction is that the piezoelectric transducer, which generally is constituted of a quite small and fragile ceramic element, may be mounted on the semi-rigid member, and thereby may be more fully protected from shock and impact than is possible when a direct attachment, linkage or coupling to the wire delay line exists. The delay line is subject to considerable vibration and shock during shipment, and during use may be inadvertently struck, or may be subject to vibration when the cabinet in which it is mounted is impacted due to carelessness. Where the transducer is secured to or coupled with a structure which has a greater mass per unit length than the delay line itself, i.e. a massive semirigid structure, instead of the highly resilient structure of the delay line itself, wavelengths in the semi-rigid structure may be considerably longer than those in the delay line for the same frequency. Primarily this effect occurs because the semi-rigid structure has a greater cross-sectional area than does the delay line. In any event, the dilference in wavelength must be accounted for in selecting velocity nodes, and in selecting lengths of transducers.

Referring now more specifically to FIGURE 4 of the accompanying drawing, the reference numeral denotes a rigid mounting, i.e. one which is not susceptible to vibrations or will not substantially support vibrations. Secured to the rigid support 20 is a semi-rigid support 21 in the form of a relatively heavy short rod of metallic material. The device 21 is described as semi-rigid because it is capable of supporting vibrations, and yet is sufiiciently rigid to withstand impact well, and is far more rigid than is the Wire 22, to which it is secured in end to end fashion.

The wire 22 constitutes a delay line to which transverse vibrations are to be imparted from the semi-rigid member 21. Tothe latter is cemented a piezo-electric crystal 23. In the structure of FIGURE 4 the piezo-electric transducer 23.is cemented along its entire length to a fiat area on the semi-rigid member 21. In the embodiment of our invention illustrated in FIGURE 5 of the accompanying drawing the transducer 24 is secured to the semirigid member 21 over only a portion of its length 25, the remainder of the transducer vibrating free. The transducers 23, 24 may each be /2 wavelength or less in length at the wavelength of the transverse vibrations existing in the semi-rigid element 21, which for a given frequency supports, longer wavelengths than does the wire 22.

Signal input or output leads 26 may in each case be secured to the semi-rigid member and to one electrode of the transducers 23, 24, at velocity nodes, and the spacing between the ends of the transducers 23, 24 and the rigid support 20 may be equal approximately to an odd member of wavelengths.

In the system of FIGURE 6 the transducer 30 is rigidly secured at one end to the rigid support 20 and the semi-rigid element 21 is similarly secured at one end of the rigid support 20, the transducer 30 and the semirigid element 21 preferably extending parallel to one another, although this is not essential to the concept. A thin Wire coupling element extends between the transducer 30 at a suitable point 33, thereof to the semi-rigid element 21 at a node 34 thereof. The point 34 may be an odd number of wavelengths, preferably unity, from the rigid support 20.

In each of FIGURES 4, 5, and 6 the transducer is physically separated from the wire delay line 22, by the interposition of the semi-rigid element 21, so that im- 6 pacts or shocks imparted to the delay line 22 cannot be communicated to the transducers but instead are transmitted to the rugged semi-rigid element 21.

What we claim is:

1. In combination, a long wire delay line, a piezoelectric transducer, and a linkage extending from a point of said transducer to a point of said long wire delay line, a clamping device for said long wire delay line, said last named point being located approximately an odd number of quarter wavelengths distance from said clamping device at an operating frequency of said long wire delay line.

2. The combination according to claim 1 wherein said clamping device is located at an effective end point of said long wire delay line.

3. The combination according to claim 1 wherein said clamping device is located remotely of the effective end of said long wire delay line and wherein said point of said long Wire delay line exists between the clamping device and the end of the long wire delay line.

4. The combination according to claim 1 wherein said odd number is unity.

5. The combination according to claim 1 wherein said transducer is end mounted and is vibrated in the transverse mode.

6. In combination, a long wire delay line, a piezoelectric transducer, a semi-rigid member having a greater mass per unit length than said long wire delay line and having a pair of opposed ends, a rigid substantially non-vibrational member, means securing said semi-rigid member at one of said ends to said rigid member so that the other end thereof is capable of supporting free vibrations, means vibrationally coupling said long wire delay line at essentially one point only to said semirigid member along said vibration supporting portion thereof, and means for vibrationally coupling said transducer to said semi-rigid member along said vibration supporting portion thereof, said semi-rigid member thereby providing a transverse vibrational coupling between said transducer and said long wire delay line and providing a high acoustic impedance to the transmission of impacts therethrough.

7. The combination according to claim 6 wherein said transducer is cemented to said semi-rigid member.

8. The combination according to claim 6 wherein said transducer is mounted on said rigid member, and wherein said means for vibrationally coupling said transducer to said semi-rigid member comprises a linkage connected to said semi-rigid member an odd number of quarter wavelengths from said rigid member at the operating frequency of said delay line.

9. In combination, a long wire delay line, a piezoelectric supersonic transducer vibrative in the transverse mode, a relatively rigid member, means securing said long wire delay line to said relatively rigid member to terminate said delay line in substantially infinite impedance, and means coupling said transducer to said delay line for transferring vibrations therebetween at impedances approaching a matched condition at the operating frequency of said delay line, said coupling means providing a shockabsorbing portion to prevent the application of impacts to said transducer via said delay line.

10. In combination, a long wire delay line, a piezoelectric transducer vibrative in the transverse mode, a cou pler comprising a bent rod having smaller diameter than the diameter of said wire and coupling said long wire delay line to said piezo-electric transducer, said coupler being unresponsive to shock and impact but responsive to ultrasonic vibrations.

11. In combination, a long Wire delay line, a piezoelectric transducer vibrative in the transverse mode, a coupler coupling said long wire delay line to said piezoelectric transducer, said coupler being unresponsive to shock and impact but responsive to ultrasonic vibrations, wherein said coupler is a massive semi-rigid element capable of transferring transverse supersonic vibrations and having a greater mass per unit length than said wire.

12. The combination according to claim 11 wherein said transducer is cemented to said semi-rigid element.

13. The combination according to claim 11 wherein said transducer is linked to said semi-rigid element.

14. In combination a long wire mechanical delay line, a transversely vibrating piezo-electric transducer, and a linkage between one point of said 'wire and one point of said transducer, wherein is further provided a rigid mounting' block, said wire and said transducer being secured to points spaced apart on said mounting block, said wire thereby being terminated at said mounting block in a relatively high acoustic impedance, said transducer having a free-vibrational portion extending from said mounting block, said linkage providing a substantially matched vibrational impedance coupling between said free vibrational portion of said transducer and said' wire at the operating frequency of said delay line.

15. The combination according to claim 14 wherein said References ciaab the Examiner HERMAN KARL SAALBACH, Primary Examiner. 

10. IN COMBINATION, A LONG WIRE DELAY LINE, A PIEZOELECTRIC TRANSDUCER VIBRATIVE IN THE TANSVERSE MODE, A COUPLER COMPRISING A BENT ROD HAVING SMALLER DIAMETER THAN THE DIAMETER OF SAID WIRE AND COUPLING SAID LONG WIRE DELAY LINE TO SAID PIEZO-ELECTRIC TRANSDUCER, SAID COUPLER BEING UNRESPONSIVE TO SHOCK AND IMPACT BUT RESPONSIVE TO ULTRASONIC VIBRATIONS. 